1. Field of the Invention
This invention is in the field of web forming processes and apparatus wherein a stock suspension is injected between a pair of traveling twin wires passing onto an imperforate rotatable roll. The present invention is particularly concerned with providing a pressurized air film for handling water drained from the roll former.
2. Description of the Prior Art
The following examples of prior art are submitted as representative but not as totally inclusive of the pertinent prior art in this field.
U.S. Pat. No. 3,056,719 provides a method and apparatus for producing a continuous paper sheet in which fibers in a liquid suspension are injected in the form of a jet of controlled size to the juncture between a rotating body and a yielding cooperating body, at least one of which has surfaces which are porous, thereby providing a zone extending the length of the juncture between the two. One of the bodies is rotated in the same direction as the jet, and the yielding body is tensioned to exert pressure for the other. The dynamics of the jet are such as to cause the suspension to penetrate forcibly between the two bodies thereby deflecting the yielding body. Constant tension is maintained during such deflection. Finally, the stock suspension is drained to produce a web of successively variable thickness, which web is then dried.
U.S. Pat. No. 3,150,037 describes a paper making machine using a centrifugal dewatering process. The method involves effecting rapid changes in the direction of a wet paper web while it is traveling at a relatively high speed on a foraminous carrier wire. The rapid changes in direction cause a substantial amount of the free moisture contained in the wet web to be ejected from the web by centrifugal action, while the forming wire supports the web so that it is not physically damaged due to the forces applied to the web during changes in direction. There is also a disclosure of the technique of injecting streams of air at relatively high velocity through the web to facilitate further dewatering.
U.S. Pat. No. 3,311,533 describes a dual forming wire type paper making apparatus. Two forming wires are provided which converge to provide an entrance nip for the reception of stock. In one zone, water is expressed in one direction and is collected in a suitable receptacle, and water is expressed in the other direction onto a forming wire which stores the water and transfers it to a location remote from the bands. At such location, the water is removed to a suitable receptacle, and the foraminous bands travel in contact with each other to a second zone in which the bands are in contact with the periphery of a second foraminous cylinder. An outwardly acting air flow is directed at a relatively low pressure differential at the second foraminous cylinder. In a succeeding zone, there is provided an inwardly acting air flow at a high pressure differential.
U.S. Pat. No. 3,565,757 describes an apparatus for forming and dewatering a fibrous web comprising a pair of spaced rotatable rolls, and an endless foraminous belt which is trained around portions of the two rolls and runs in a straight line between them. A second forming wire runs generally conjointly with the first forming wire around the first roll so that it defines an inlet space with the first belt in which stock in the form of a ribbon-like jet is fed. The second belt moves conjointly with the first belt along a part of the straight run from the first to the second roll and is then trained around a guide roll and separated from the first belt leaving the web on the upper surface of the first belt. The stock is dewatered in the forming zone and is formed into a web by the combination of centrifugal force and by the pressure of the outer belt against the stock resulting from the tension of the outer belt. Further dewatering is accomplished along the straight run from the forming roll to the second roll by one or more pressure or section boxes disposed along such straight run and creating a pressure differential across the web. The first and second rolls are arranged with respect to the belt such that the first belt runs to a couch roll with the web carried on its upper surface. The web is taken off the first belt somewhere along a free run after it turns around the second roll.
U.S. Pat. No. 3,844,881 describes still another multi-layer paper web forming system in which a first slurry is delivered onto a moving wire opposite a section forming roll and a second slurry is deposited on the first slurry downstream of the forming roll. A second suction roll is positioned downstream of the second slurry discharge adjacent the paper web side of the screen around which the endless screen is wrapped in an arcuate path. The second suction roll may be wrapped in part by a second endless forming screen which may then travel away from the second suction roll in conjunction with the first endless forming screen.
U.S. Pat. No. 3,876,498, assigned to the same assignee as the present invention, deals with a method and apparatus for continuously forming a fibrous web from a slurry of stock. The stock is injected as a jet between two woven forming wires positioned to travel over a solid impermeable roll. A headbox is provided with trailing self-positionable elements to deliver stock to the forming throat. At the end of the forming run, the outer wire is separated from the inner wire at a separation point with a small angle between the two. The outer wire is cleaned at the separation point, and the web follows the inner wire despite the centrifugal force present on it.
Finally, U.S. Pat. No. 4,028,174 describes an apparatus for collecting liquids thrown from a moving web former. It provides a series of curved deflectors which intercept the high velocity sprays thrown from such forming member, the deflectors having holes remote from the forming member for permitting substantially all the liquid collected by the deflector to pass through the holes and in so doing to be substantially slowed in velocity. This substantially elimininates aeration from splashing and is said to considerably reduce the noise.